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Passive House office buildings are certified by the Passive House Institute (PHI) based on a standard occupancy level and corresponding internal gains of 3.5 W/m² (the reference area being the “treated floor area” of the PHPP, not the office area). From the PHI’s experience this value represents a typical average, taking into account an improved efficiency of the equipment used. The reasons why the PHI uses standard values for certification are partly to be able to ensure consistency and also because the use of a building is often not permanent and not always prior known.
A certain pattern of usage may change after a couple of years but the building fabric will last for several decades; the certified building must perform as a Passive House under all circumstances that can reasonably be assumed within this time span. By planning the building for a typical use, a high level of efficiency is reached over the entire lifetime of the building. Another important reason is the incentive for the user to reduce the internal gains even if the occupancy level is higher than the standard assumption. This is very significant for the overall performance, as heating the building with losses from office equipment and lighting is equivalent to direct electric heating, which is very disadvantageous solution in terms of the primary energy demand and will also impair the thermal comfort in summer:
A higher occupancy level essentially leads to higher internal gains, which means that the 15 kWh/(m²a) Passive House criteria is in theory easier to reach. On the other hand, it can cause problems during hot summer periods. It is important to take the higher occupancy and actual internal gains into account during the planning stage - additional measures (e.g. more night time ventilation, automated shading etc.) might be needed to ensure summer comfort. The same PHPP can be used to calculate both scenarios, based on the standard (for certification) and the expected internal gains. Additional measures that might need to be taken to reach the Passive House certification with the standard internal gains will not be counterproductive for the higher occupancy level. In any case the internal gains should be reduced as far as possible by using efficient equipment, external shading etc. and any excess heat during summer can only be effectively removed from the building by means of ventilation (esp. night flushing).
In very special cases, if it is clear that the occupancy is highly unlikely to change over the lifetime of the building or if the use of the building significantly differs from a typical office environment, exceptions may be made as to the internal gains used for the certification as a Passive House.